The present invention relates to an electronic component which is preferably used in, for example, an electronic apparatus conducting radio communication, such as a mobile communication terminal or a personal computer, and which compositely includes an inductor and a capacitor.
In a cordless telephone or a cellular telephone, in order to lower the cost and miniaturize the telephone, it is requested to reduce the sizes and number of components. In a portable electronic apparatus such as a notebook personal computer, data communication using a wireless LAN or the like is often conducted, and hence also components in such an electronic apparatus are requested to be reduced in size and number.
In such communication, an electronic component which compositely includes an inductor and a capacitor is necessary. Electronic components of this kind are often used as various filter circuits in a radio communication circuit for the purpose of selectively allowing a signal in a desired frequency band to pass therethrough, and attenuating an unwanted signal. Filters include a band-pass filter through which only a signal in a specific frequency band can be passed, a low-pass filter through which only a signal in a lower frequency band can be passed, and a high-pass filter through which only a signal in a higher frequency band can be passed.
Conventionally, a filter is sometimes configured by using an inductor component and a capacitor component which are discrete chip components, to form an LC circuit on a circuit board of a wireless apparatus. Also a dielectric filter and a surface acoustic wave filter which are configured respectively by single elements, and a composite electronic component having a filter function of a dielectric filter, such as a multilayer LC filter are used. In order to cope with various frequency characteristics, particularly, a multilayer LC filter is often used in an electronic component.
FIG. 30 is a section view of a multilayer LC filter of the conventional art, and FIG. 31 is a perspective view of a multilayer LC filter of the conventional art. (See, for example, JP-A-2000-341069 or JP-A-1-259518)
Attenuation characteristics and attenuation curve characteristics which are required in a filter are determined by an equivalent circuit of an inductor component L and a capacitor component C, and their values. When one of the values of the components is changed, it is possible to obtain desired filter characteristics. In order to realize a filter which can be used in the GHz band or the like, an impedance of a certain level or higher is required, and therefore, the inductor value or the capacitor value must be adequately controlled.
In the case where a filter is configured by a laminated element, however, the inductor component L is formed by printing or the like in a laminated member, and hence the value is inevitably small. In order to obtain necessary attenuation characteristics, therefore, the capacitor component must be increased. As a result, the material of the laminated member must be improved, and the number of laminations in the laminated member must be increased, so that the production step number and the cost are additionally required, thereby causing a problem in that the reductions of the size and the cost are inevitably limited.
In an element in which miniaturization of a certain level is requested, moreover, there is a problem in that further size reduction is naturally limited.
In pattern printing for producing an inductor component, for example, a printed pattern which is to be formed in a laminated member to produce an inductor component must be formed before a process of firing the laminated member, and hence problems such as that the value of the inductor component is unavoidably changed after a lamination process occur. Therefore, it is difficult to realize a highly accurate filter.
In a conventional electronic component such as a multilayer LC filter, as seen from the section view of FIG. 30, electrodes are configured inside a ceramic member, and hence complicated production steps must be conducted, so that it is difficult to reduce the cost. Because the production steps are complicated and the step number is increased, the steps have many causes of dispersing characteristics. In joining to an external circuit, although the impedance must be matched with that of a circuit pattern on a circuit board, circuit constants in a filter cannot be finely adjusted, and hence an external matching circuit is additionally required. As a result, it is difficult to reduce the size of a portable terminal.
As apparent also from the perspective view of FIG. 31, the inductance is configured in a planar form. In order to obtain a large inductance value, therefore, a large pattern must be formed, thereby causing a problem in that it is difficult to suppress an electronic component to a small size.
By contrast, when an LC circuit is configured by discrete chip components, arbitrary circuit constants can be obtained, and the degree of freedom in design of a circuit on a circuit board is enhanced. However, the number of components is larger than that in the case where a composite component is used, thereby causing a problem in that the mounting area is widened and a circuit board and hence an electronic apparatus are hardly miniaturized. Of course, there is a further problem in that the large number of components causes the cost to be increased.
In an attenuation curve showing filter characteristics, a pole is formed. It is requested to obtain desired attenuation characteristics by adjusting the formation of a pole. In order to realize this, the inductor and capacitor components must be adjusted. In a conventional laminated component, it is difficult to conduct this adjustment, and there is a problem in that such adjustment of the inductor and capacitor components may not result in adjustment of the formation of a pole, but in variation of the cutoff frequency.